The long-term goals of this research program are to define mechanisms of Sjogren's syndrome (SS) as a way to impact disease therapy, prediction and prevention. SS is a systemic autoimmune disease, which predominantly affects salivary and lacrimal glands, leading to significant morbidity. Occurring alone (primary) or in the context of other systemic rheumatic diseases (e.g. Rheumatoid arthritis, SLE - 'secondary'), the causes and mechanisms of SS remain obscure, and therapy remains empirical and symptom-focused. The autoimmune rheumatic diseases share significant mechanistic similarity in terms of amplification and tissue damage, making discoveries about initiation and propagation of SS broadly relevant.( The striking association of unique autoimmune responses with specific/phenotypes is of significant diagnostic and prognostic value, and provides a major clue to disease mechanism. Human disease tissue and immune markers provide important tools to interrogate disease mechanism. In previous studies, we have observed striking and specific alterations in the structure of autoantigens during various forms of cell death. We have also recently described markedly enhanced autoantigen expression in the target tissues in myositis, particularly in regenerating muscle cells. Similar findings have recently been made in SS salivary glands. Our data has also identified an important but previously unrecognized similarity between molecular pathways of differentiation and the type I interferon signature noted to be present in SLE, myositis and SS. In this R37 continuation, (i) we will investigate the cell types and differentiation states that express increased autoantigen levels directly in SS biopsies. We will investigate SS autoantigen expression in various differentiating cell models relevant to systemic rheumatic diseases, including hematopoietic and muscle stem cells, and salivary and other epithelial cells. We will use microarray-based transcriptional profiling to define the pathways upstream of antigen expression, and any forces that restrain full differentiation. These studies will identify the source and mechanisms of antigen drive in SS and other rheumatic diseases; (ii) We will extend our studies to define the effects of various cytotoxic lymphocyte granule components on epithelial cell structure and function, with a particular focus on defining mechanisms underlying the effects of human granzymes, and demonstrating these events in SS tissue; (iii)We will address whether regenerating cells provide a source of endogenous ligands for innate immune receptors (e.g. Toll-like receptors) both in vitro and in vivo , and thereby play a dual role in driving systemic autoimmunity. Together, these studies will define novel pathways critical to SS and other rheumatic diseases, with significant therapeutic potential.